A light emitting diode (LED) typically includes a base, a light emitting die and a lamp. The light emitting die is positioned on the base and embedded in the lamp. The light generated by the light emitting die is transmitted through the lamp and emitted from the lamp as output light.
A significant goal in designing an LED is to increase the brightness of the LED. Brightness is optically defined as the amount of flux or power emitted from an area into a solid angle (brightness=flux/(area×solid angle)). One approach to increase the brightness of an LED is to use a light emitting die having higher emission efficiency. The higher emission efficiency of the light emitting die increases the flux, which results in an increased brightness of the LED. A concern with this approach is that the use of such a light emitting die may not be cost-effective for mass-production of LEDs.
Another approach to increase the brightness of an LED is to use the geometrical shape of the lamp. For example, the lamp may be shaped to include a convex region on top of a cylindrical body. The convex region functions as a lens to reduce the angular divergence of the emitted light from the light emitting die, which increases the brightness of the LED. However, the effectiveness of such a lamp on the brightness of the LED depends on the amount of light that reaches the convex region of the lamp at desired angles. The light that reaches the convex region of the lamp at large diverging angles may not contribute to the reduction of angular divergence of emitted light. Since the light generated by the light emitting die is initially emitted in all directions, more light will reach the convex region of the lamp at desired angles if the convex region is enlarged. However, such a modification of the lamp may be constrained by miniaturization requirements of LEDs for common applications.
In view of these concerns, what is needed is a device and method for emitting light with increase brightness that is cost-effective and can satisfy miniaturization requirements for common applications.